Optical film, laminated polarizing plate, liquid crystal display using the same, and self-light-emitting display using the same

ABSTRACT

The present invention provides a transparent optical film that has excellent optical characteristics for realizing the uniform retardation distribution and restraining rainbow-colored irregularities. The optical film, which is obtained by laminating a birefringent layer (a) on a transparent film (b), satisfies all the following formulae (I), (II) and (III).
 
Δ n ( a )&gt;Δ n ( b )×10  (I)
 
1&lt;( nx−nz )/( nx−ny )  (II)
 
0.0005&lt;Δ n ( a )≦0.5  (III)
In the above formulae (I), (II) and (III), Δn(a) and Δn(b) denote respectively birefringent indexes of the birefringent layer (a) and the transparent film (b). The signs of nx, ny and nz indicate refractive indexes in an X-axis direction, a Y-axis direction and a Z-axis direction in the birefringent layer (a), respectively. The X-axis corresponds to an axial direction exhibiting a maximum refractive index within a plane of the birefringent layer (a), the Y-axis corresponds to an axial direction perpendicular to the X-axis within the plane, and the Z-axis corresponds to a thickness direction perpendicular to the X-axis and the Y-axis.

TECHNICAL FIELD

The present invention relates to an optical film, a laminated polarizingplate comprising the optical film laminated thereon, and a liquidcrystal display and a self-light-emitting display using the same.

BACKGROUND ART

Conventionally, retardation plates have been used for the purpose ofoptical compensation in various liquid crystal displays. For suchretardation plates, for example, optical biaxial retardation plates areused. The biaxial retardation plates can be manufactured by variouskinds of polymer film stretching techniques such as roller tensilestretching, roller press stretching, and tenter transverse uniaxialstretching (for example, see JP 3(1991)-33719 A), and also manufacturedby the technique of biaxial stretching to provide an anisotropy (forexample, refer to JP 3(1991)-24502 A), or the like. Other examplesinclude a retardation plate including both a uniaxially stretchedpolymer film having a positive optical anisotropy and a biaxiallystretched polymer film having a negative optical anisotropy with a smallin-plane retardation value (see JP 4(1992)-19482A). Alternatively, aretardation plate provided with a negative uniaxiality can bemanufactured not by any of the above-mentioned stretching methods but byusing the property of polyimide so as to process a soluble polyimideinto a film on a substrate (JP 8(1996)-511812 A).

Stretched films formed by the above-described film-stretching techniquesare provided, for example, with an optical characteristic nx>ny>nz.Here, nx, ny, nz indicate refractive indexes in an X-axis direction, aY-axis direction and a Z-axis direction, respectively. The X-axiscorresponds to an axial direction exhibiting a maximum refractive indexwithin a plane of the film, the Y-axis corresponds to an axial directionperpendicular to the X-axis within the plane, and the Z-axis correspondsto a thickness direction perpendicular to the X-axis and the Y-axis.When arranged between a liquid crystal cell and a polarizer of a liquidcrystal display, a birefringent film having the above-stated opticalcharacteristics can widen a viewing angle of the liquid crystal display,and thus the birefringent film is useful as a viewing angle compensatingfilm for the liquid crystal cell.

DISCLOSURE OF THE INVENTION

However, when a film with the above-mentioned optical characteristic isapplied to a liquid crystal display, it has a problem of arainbow-colored irregularity, although it has an advantage of a sharpcontrast in a wide viewing angle.

Accordingly, an object of the present invention is to provide an opticalfilm with a negative birefringence, which can prevent therainbow-colored irregularity and provide an excellent display property,for example, when it is applied to various display apparatuses such asliquid crystal displays.

For achieving the object, an optical film of the present inventionrefers to an optical film comprising a birefringent layer (a) and atransparent film (b), in which the birefringent layer (a) is laminatedon the transparent film (b) and all the following formulae (I), (II) and(III) are satisfied.Δn(a)>Δn(b)×10  (I)1<(nx−nz)/(nx−ny)  (II)0.0005≦Δn(a)≦0.5  (III)

Here, Δn(a) and Δn(b) in the above formulae (I), (II) and (III) arebirefringent indexes of the birefringent layer (a) and the transparentfilm (b) respectively, and each of Δn(a) and Δn(b) is represented by thefollowing equations. In the above formula (II) and the equations below,nx, ny and nz indicate refractive indexes in an X-axis direction, aY-axis direction and a Z-axis direction in the birefringent layer (a),respectively. Similarly, nx′, ny′ and nz′ indicate refractive indexes inan X-axis direction, a Y-axis direction and a Z-axis direction in thetransparent film (b), respectively. The X-axis corresponds to an axialdirection exhibiting a maximum refractive index within a plane of thebirefringent layer (a) and the transparent film (b), the Y-axiscorresponds to an axial direction perpendicular to the X-axis within theplane, and the Z-axis corresponds to a thickness direction perpendicularto the X-axis and the Y-axis.Δn(a)=[(nx+ny)/2]−nzΔn(b)=[(nx′+ny′)/2]−nz′

As a result of earnest studies, inventors of the present invention foundthat the above-mentioned conventional problems can be solved when anoptical film including a birefringent layer laminated on a transparentfilm satisfies all the conditions shown by the formulae (I), (II) and(III), leading to the present invention. More specifically, when, forexample, optical films satisfying all the formulae (I), (II) and (III)are used in various display apparatuses such as liquid crystal displays,they provides a sharp contrast in the wide viewing angle andfurthermore, they can prevent a rainbow-colored irregularity caused bydepolarization, and thus a higher display quality is provided. Asdescribed below, this optical film can be manufactured by coating apolymer material such as polyimide directly onto the transparent film.Therefore, for example, there is no need to transcribe the birefringentlayer on any other substrate or the like after formation of thebirefringent layer on the transparent film, but the birefringent layeritself can be used as a laminate. Thus, the optical film of the presentinvention is excellent in uniformity of quality, workability or thelike. Accordingly, since the optical film of the present invention isuniform and transparent and it has an excellent optical characteristicfor a negative birefringent effect of nx>ny>nz, the optical film issuitably used for a laminated polarizing plate, a liquid crystal paneland various image display apparatuses such as a liquid crystal displayand a self-light-emitting display.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing optical axial directions accordingto the present invention.

FIG. 2 is a cross-sectional view of an example of a laminated polarizingplate of the present invention.

FIG. 3 is a cross-sectional view of another example of a laminatedpolarizing plate of the present invention.

FIG. 4 is a cross-sectional view of an example of a liquid crystal panelof the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As stated above, an optical film of the present invention includes an abirefringent layer (a) and a transparent film (b), in which thebirefringent layer (a) is laminated on the transparent film (b), and allof the formulae (I), (II) and (III) are satisfied.

In the present invention, since optical compensation is primarilycarried out in the birefringent layer (a), it is necessary to satisfythe formula (I) so that the birefringent effect of the transparent film(b) may not prevent the optical compensation. By satisfying the formula(I), rainbow-colored irregularities caused by the depolarization isprevented, thus further excellent display properties can be obtained.For further improving viewing angle compensation and display properties,it is preferable, for example, that the relation between the Δn(a) andΔn(b) satisfies Δn(a)>Δn(b)×15, or more preferably, Δn(a)>Δn(b)×20.

In the present invention, it is required that the birefringent layer (a)satisfies the formula (II). When an optical film of the presentinvention satisfies 1<(nx−nz)/(nx−ny), a birefringent index in athickness direction becomes larger than a birefringent index within aplane of the film, so as to improve, for example, an opticalcompensation of a liquid crystal cell. It is more preferable to satisfy1<(nx−nz)/(nx−ny)≦100. If the value of (nx−nz)/(nx−ny) is 100 orsmaller, for example, when the optical film of the present invention isapplied to a liquid crystal display, a sufficient contrast ratio can beobtained, thus an excellent viewing angle property is realized.Furthermore, in order to obtain an excellent optical compensation, thevalue of (nx−nz)/(nx−ny) is more preferably in the range of1<(nx−nz)/(nx−ny)≦80, and further preferably in the range of1≦(nx−nz)/(nx−ny)≦50. For application to a liquid crystal display ofvertical aligned (VA) mode, particularly preferable range is1≦(nx−nz)/(nx−ny)≦30.

In the schematic figure of FIG. 1, optical axis directions of refractiveindexes (nx, ny, nz) in a birefringent layer (a) 10 are shown by arrows.As mentioned above, nx, ny and nz indicate refractive indexes in anX-axis direction, a Y-axis direction and a Z-axis direction,respectively. The X-axis corresponds to an axial direction exhibiting amaximum refractive index within a plane of the film, the Y-axiscorresponds to an axial direction perpendicular to the X-axis within theplane, and the Z-axis corresponds to a thickness direction perpendicularto the X-axis and the Y-axis.

In the present invention, it is further necessary that the birefringentlayer (a) satisfies the above-described formula (III) because of thefollowing reason. When the Δn(a) is lower than 0.0005, an optical filmincreases in thickness. When the Δn(a) is larger than 0.5, controllingof a phase difference will be difficult. More preferably, the refractiveindex is in the range of 0.005≦Δn(a)≦0.2, and particularly preferably,in the range of 0.02≦Δn(a)≦0.15.

In the present invention, the thickness of the birefringent layer (a) isnot particularly limited, but in order to obtain a thin liquid crystaldisplay and also an optical film having an excellent viewing anglecompensating function and a uniform phase difference, the thickness ofthe birefringent layer (a) preferably ranges from 0.1 to 50 μm, morepreferably from 0.5 to 30 μm, or further preferably, from 1 to 20 μm.The thickness of the transparent film (b) can be determined according tothe use or the like, however, in terms of the strength and decrease inthe thickness of the layer, a preferable range for the thickness of thetransparent film (b) is from 5 to 500 μm, or more preferably, from 10 to200 μm, or further preferably, from 15 to 150 μm.

The birefringent layer (a) can be laminated on one or both surface(s) ofthe transparent film (b), and the laminate can include one or plurallayer(s). The transparent film (b) can be a single layer or a laminateof plural layers. If the transparent film is a laminate, it can becomposed of one or various kind(s) of polymer layers, depending on itsuses such as the improvement in strength, heat resistance and adhesionof birefringent layers.

A material of the birefringent layer (a) is not specifically limited, aslong as it satisfies all the above-stated conditions, but in order tosatisfy the formula (I), the kind of the material is preferablyselected, for example, according to the material of the transparent filmmentioned below. In the selection, for example, it is preferable thatthe birefringent index of the birefringent layer formed by using thematerial is relatively high, while the following transparent film (b) isformed of a material that is selected to provide a relatively lowbirefringent index to the birefringent layer.

The material of the birefringent layer is preferably a non-liquidcrystalline material, more preferably a non-liquid crystalline polymer.Unlike a liquid crystalline material, for example, such a non-liquidcrystalline material forms a film that shows an optical uniaxiality ofnx>nz, and ny>nz due to its character regardless of the orientation of asubstrate. Therefore, a substrate to be used is not limited to anoriented substrate, and the processes such as coating an oriented filmand laminating an oriented film on its surface, can be omitted even if anon-oriented substrate is used.

The non-liquid crystalline polymer preferably is a polymer such aspolyamide, polyimide, polyester, polyetherketone, polyamideimide andpolyesterimide because of its excellent heat resistance, chemicalresistance, transparency and hardness. It may be possible to use one ofthese polymers alone or a mixture of two or more polymers havingdifferent functional groups, for example, a mixture ofpolyaryletherketone and polyamide. Among these polymers, polyimide isparticularly preferable because a high transparency, a high orientation,and a high stretch property can be obtained.

The molecular weight of the above-mentioned polymer is not particularlylimited, but the weight-average molecular weight (Mw) thereof preferablyranges from 1,000 to 1,000,000 and more preferably ranges from 2,000 to500,000.

As the polyimide, it is preferable to use a polyimide that has a highin-plane orientation and is soluble in an organic solvent. For example,it is possible to use a condensation polymer of9,9-bis(aminoaryl)fluorene and an aromatic tetracarboxylic dianhydridedisclosed in JP 2000-511296 A, more specifically, a polymer containingat least one repeating unit represented by the formula (1) below.

In the above formula (1), R³ to R⁶ are at least one substituent selectedindependently from the group consisting of hydrogen, halogen, a phenylgroup, a phenyl group substituted with 1 to 4 halogen atoms or a C₁₋₁₀alkyl group, and a C₁₋₁₀ alkyl group. Preferably, R³ to R⁶ are at leastone substituent selected independently from the group consisting ofhalogen, a phenyl group, a phenyl group substituted with 1 to 4 halogenatoms or a C₁₋₁₀ alkyl group, and a C₁₋₁₀ alkyl group.

In the above formula (1), Z is, for example, a C₆₋₂₀ quadrivalentaromatic group, and preferably is a pyromellitic group, a polycyclicaromatic group, a derivative of a polycyclic aromatic group or a grouprepresented by the formula (2) below.

In the formula (2) above, Z′ is, for example, a covalent bond, a C(R⁷)₂group, a CO group, an O atom, an S atom, an SO₂ group, an Si(C₂H₅)₂group or an NR⁸ group. When there are plural Z's, they may be the sameor different. Also, w is an integer from 1 to 10. R⁷s independently arehydrogen or C(R⁹)₃. R⁸ is hydrogen, an alkyl group having from 1 toabout 20 carbon atoms or a C₆₋₂₀ aryl group, and when there are pluralR⁸s, they may be the same or different. R⁹s independently are hydrogen,fluorine or chlorine.

The above-mentioned polycyclic aromatic group may be, for example, aquadrivalent group derived from naphthalene, fluorene, benzofluorene oranthracene. Further, a substituted derivative of the above-mentionedpolycyclic aromatic group may be the above-mentioned polycyclic aromaticgroup substituted with at least one group selected from the groupconsisting of, for example, a C₁₋₁₀ alkyl group, a fluorinatedderivative thereof and halogen such as F and Cl.

Other than the above, homopolymer whose repeating unit is represented bythe general formula (3) or (4) below or polyimide whose repeating unitis represented by the general formula (5) below disclosed in JP8(1996)-511812 A may be used, for example. The polyimide represented bythe formula (5) below is a preferable mode of the homopolymerrepresented by the formula (3).

In the above general formulae (3) to (5), G and G′ each are a groupselected independently from the group consisting of, for example, acovalent bond, a CH₂ group, a C(CH₃)₂ group, a C(CF₃)₂ group, a C(CX₃)₂group (wherein X is halogen), a CO group, an O atom, an S atom, an SO₂group, an Si(CH₂CH₃)₂ group and an N(CH₃) group, and G and G′ may be thesame or different.

In the above formulae (3) and (5), L is a substituent, and d and eindicate the number of substitutions therein. L is, for example,halogen, a C₁₋₃ alkyl group, a halogenated C₁₋₃ alkyl group, a phenylgroup or a substituted phenyl group, and when there are plural Ls, theymay be the same or different. The above-mentioned substituted phenylgroup may be, for example, a substituted phenyl group having at leastone substituent selected from the group consisting of halogen, a C₁₋₃alkyl group and a halogenated C₁₋₃ alkyl group. Also, theabove-mentioned halogen may be, for example, fluorine, chlorine, bromineor iodine. d is an integer from 0 to 2, and e is an integer from 0 to 3.

In the above formulae (3) to (5), Q is a substituent, and f indicatesthe number of substitutions therein. Q may be, for example, an atom or agroup selected from the group consisting of hydrogen, halogen, an alkylgroup, a substituted alkyl group, a nitro group, a cyano group, athioalkyl group, an alkoxy group, an aryl group, a substituted arylgroup, an alkyl ester group and a substituted alkyl ester group and,when there are plural Qs, they may be the same or different. Theabove-mentioned halogen may be, for example, fluorine, chlorine, bromineor iodine. The above-mentioned substituted alkyl group may be, forexample, a halogenated alkyl group. Also, the above-mentionedsubstituted aryl group may be, for example, a halogenated aryl group. fis an integer from 0 to 4, and g and h respectively are an integer from0 to 3 and an integer from 1 to 3. Furthermore, it is preferable that gand h are larger than 1.

In the above formula (4), R¹⁰ and R¹¹ are groups selected independentlyfrom the group consisting of hydrogen, halogen, a phenyl group, asubstituted phenyl group, an alkyl group and a substituted alkyl group.It is particularly preferable that R¹⁰ and R¹¹ independently are ahalogenated alkyl group.

In the above formula (5), M¹ and M² may be the same or different and,for example, halogen, a C₁₋₃ alkyl group, a halogenated C₁₋₃ alkylgroup, a phenyl group or a substituted phenyl group. The above-mentionedhalogen may be, for example, fluorine, chlorine, bromine or iodine. Theabove-mentioned substituted phenyl group may be, for example, asubstituted phenyl group having at least one substituent selected fromthe group consisting of halogen, a C₁₋₃ alkyl group and a halogenatedC₁₋₃ alkyl group.

A specific example of polyimide represented by the formula (3) includespolyimide represented by the formula (6) below.

Moreover, the above-mentioned polyimide may be, for example, copolymerobtained by copolymerizing acid dianhydride and diamine other than theabove-noted skeleton (the repeating unit) suitably.

The above-mentioned acid dianhydride may be, for example, aromatictetracarboxylic dianhydride. The aromatic tetracarboxylic dianhydridemay be, for example, pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, naphthalene tetracarboxylic dianhydride,heterocyclic aromatic tetracarboxylic dianhydride or 2,2′-substitutedbiphenyl tetracarboxylic dianhydride.

The pyromellitic dianhydride may be, for example, pyromelliticdianhydride, 3,6-diphenyl pyromellitic dianhydride,3,6-bis(trifluoromethyl)pyromellitic dianhydride,3,6-dibromopyromellitic dianhydride or 3,6-dichloropyromelliticdianhydride. The benzophenone tetracarboxylic dianhydride may be, forexample, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride,2,3,3′,4′-benzophenone tetracarboxylic dianhydride or2,2′,3,3′-benzophenone tetracarboxylic dianhydride. The naphthalenetetracarboxylic dianhydride may be, for example,2,3,6,7-naphthalene-tetracarboxylic dianhydride,1,2,5,6-naphthalene-tetracarboxylic dianhydride or2,6-dichloro-naphthalene-1,4,5,8-tetracarboxylic dianhydride. Theheterocyclic aromatic tetracarboxylic dianhydride may be, for example,thiophene-2,3,4,5-tetracarboxylic dianhydride,pyrazine-2,3,5,6-tetracarboxylic dianhydride orpyridine-2,3,5,6-tetracarboxylic dianhydride. The 2,2′-substitutedbiphenyl tetracarboxylic dianhydride may be, for example,2,2′-dibromo-4,4′,5,5′-biphenyl tetracarboxylic dianhydride,2,2′-dichloro-4,4′,5,5′-biphenyl tetracarboxylic dianhydride or2,2′-bis(trifluoromethyl)-4,4′,5,5′-biphenyl tetracarboxylicdianhydride.

Other examples of the aromatic tetracarboxylic dianhydride may include3,3′,4,4′-biphenyl tetracarboxylic dianhydride,bis(2,3-dicarboxyphenyl)methane dianhydride,bis(2,5,6-trifluoro-3,4-dicarboxyphenyl)methane dianhydride,2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride,4,4′-(3,4-dicarboxyphenyl)-2,2-diphenylpropane dianhydride,bis(3,4-dicarboxyphenyl)ether dianhydride, 4,4′-oxydiphthalicdianhydride, bis(3,4-dicarboxyphenyl)sulfonic dianhydride,(3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride),4,4′-[4,4′-isopropylidene-di(p-phenyleneoxy)]bis(phthalic dianhydride),N,N-(3,4-dicarboxyphenyl)-N-methylamine dianhydride andbis(3,4-dicarboxyphenyl)diethylsilane dianhydride.

Among the above, the aromatic tetracarboxylic dianhydride preferably is2,2′-substituted biphenyl tetracarboxylic dianhydride, more preferablyis 2,2′-bis(trihalomethyl)-4,4′,5,5′-biphenyl tetracarboxylicdianhydride, and further preferably is2,2′-bis(trifluoromethyl)-4,4′,5,5′-biphenyl tetracarboxylicdianhydride.

The above-mentioned diamine may be, for example, aromatic diamine.Specific examples thereof include benzenediamine, diaminobenzophenone,naphthalenediamine, heterocyclic aromatic diamine and other aromaticdiamines.

The benzenediamine may be, for example, diamine selected from the groupconsisting of benzenediamines such as o-, m- and p-phenylenediamine,2,4-diaminotoluene, 1,4-diamino-2-methoxybenzene,1,4-diamino-2-phenylbenzene and 1,3-diamino-4-chlorobenzene. Examples ofthe diaminobenzophenone may include 2,2′-diaminobenzophenone and3,3′-diaminobenzophenone. The naphthalenediamine may be, for example,1,8-diaminonaphthalene or 1,5-diaminonaphthalene. Examples of theheterocyclic aromatic diamine may include 2,6-diaminopyridine,2,4-diaminopyridine and 2,4-diamino-S-triazine.

Further, other than the above, the aromatic diamine may be4,4′-diaminobiphenyl, 4,4′-diaminodiphenyl methane,4,4′-(9-fluorenylidene)-dianiline,2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl,3,3′-dichloro-4,4′-diaminodiphenyl methane,2,2′-dichloro-4,4′-diaminobiphenyl, 2,2′,5,5′-tetrachlorobenzidine,2,2-bis(4-aminophenoxyphenyl)propane, 2,2-bis(4-aminophenyl)propane,2,2-bis(4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 4,4′-diaminodiphenyl ether, 3,4′-diamino diphenyl ether,1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,1,4-bis(4-aminophenoxy)benzene, 4,4′-bis(4-aminophenoxy)biphenyl,4,4′-bis(3-aminophenoxy)biphenyl,2,2-bis[4-(4-aminophenoxy)phenyl]propane,2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3,-hexafluoropropane,4,4′-diamino diphenyl thioether or 4,4′-diaminodiphenylsulfone.

The polyetherketone as a material for forming the birefringent layer (a)may be, for example, polyaryletherketone represented by the generalformula (7) below, which is disclosed in JP 2001-49110 A.

In the above formula (7), X is a substituent, and q is the number ofsubstitutions therein. X is, for example, a halogen atom, a lower alkylgroup, a halogenated alkyl group, a lower alkoxy group or a halogenatedalkoxy group, and when there are plural Xs, they may be the same ordifferent.

The halogen atom may be, for example, a fluorine atom, a bromine atom, achlorine atom or an iodine atom, and among these, a fluorine atom ispreferable. The lower alkyl group preferably is a C₁₋₆ lower straightalkyl group or a C₁₋₆ lower branched alkyl group and more preferably isa C₁₋₄ straight or branched chain alkyl group, for example. Morespecifically, it preferably is a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, an isobutyl group, a sec-butylgroup or a tert-butyl group, and particularly preferably is a methylgroup or an ethyl group. The halogenated alkyl group may be, forexample, a halide of the above-mentioned lower alkyl group such as atrifluoromethyl group. The lower alkoxy group preferably is a C₁₋₆straight or branched chain alkoxy group and more preferably is a C₁₋₄straight or branched chain alkoxy group, for example. More specifically,it further preferably is a methoxy group, an ethoxy group, a propoxygroup, an isopropoxy group, a butoxy group, an isobutoxy group, asec-butoxy group or a tert-butoxy group, and particularly preferably isa methoxy group or an ethoxy group. The halogenated alkoxy group may be,for example, a halide of the above-mentioned lower alkoxy group such asa trifluoromethoxy group.

In the above formula (7), q is an integer from 0 to 4. In the formula(7), it is preferable that q=0 and a carbonyl group and an oxygen atomof an ether that are bonded to both ends of a benzene ring are presentat para positions.

Also, in the above formula (7), R¹ is a group represented by the formula(8) below, and m is an integer of 0 or 1.

In the above formula (8), X′ is a substituent and is the same as X inthe formula (7), for example. In the formula (8), when there are pluralX's, they may be the same or different. q′ indicates the number ofsubstitutions in the X′ and is an integer from 0 to 4, preferably, q′=0.In addition, p is an integer of 0 or 1.

In the formula (8), R² is a divalent aromatic group. This divalentaromatic group is, for example, an o-, m- or p-phenylene group or adivalent group derived from naphthalene, biphenyl, anthracene, o-, m- orp-terphenyl, phenanthrene, dibenzofuran, biphenyl ether or biphenylsulfone. In these divalent aromatic groups, hydrogen that is bondeddirectly to the aromatic may be substituted with a halogen atom, a loweralkyl group or a lower alkoxy group. Among them, the R² preferably is anaromatic group selected from the group consisting of the formulae (9) to(15) below.

In the above formula (7), the R¹ preferably is a group represented bythe formula (16) below, wherein R² and p are equivalent to those in theabove-noted formula (8).

Furthermore, in the formula (7), n indicates a degree of polymerizationranging, for example, from 2 to 5000 and preferably from 5 to 500. Thepolymerization may be composed of repeating units with the samestructure or those with different structures. In the latter case, thepolymerization form of the repeating units may be a block polymerizationor a random polymerization.

Moreover, it is preferable that an end on a p-tetrafluorobenzoylenegroup side of the polyaryletherketone represented by the formula (7) isfluorine and an end on an oxyalkylene group side thereof is a hydrogenatom. Such a polyaryletherketone can be represented by the generalformula (17) below. In the formula below, n indicates a degree ofpolymerization as in the formula (7).

Specific examples of the polyaryletherketone represented by the formula(7) may include those represented by the formulae (18) to (21) below,wherein n indicates a degree of polymerization as in the formula (7).

Other than the above, the polyamide or polyester as a material forforming the birefringent layer (a) may be, for example, polyamide orpolyester described by JP 10(1998)-508048 A, and their repeating unitscan be represented by the general formula (22) below.

In the above formula (22), Y is O or NH. E is, for example, at least onegroup selected from the group consisting of a covalent bond, a C₂alkylene group, a halogenated C₂ alkylene group, a CH₂ group, a C(CX₃)₂group (wherein X is halogen or hydrogen), a CO group, an O atom, an Satom, an SO₂ group, an Si(R)₂ group and an N(R) group, and Es may be thesame or different. In the above-mentioned E, R is at least one of a C₁₋₃alkyl group and a halogenated C₁₋₃ alkyl group and present at a metaposition or a para position with respect to a carbonyl functional groupor a Y group.

Further, in the above formula (22), A and A′ are substituents, and t andz respectively indicate the numbers of substitutions therein.Additionally, p is an integer from 0 to 3, q is an integer from 1 to 3,and r is an integer from 0 to 3.

The above-mentioned A is selected from the group consisting of, forexample, hydrogen, halogen, a C₁₋₃ alkyl group, a halogenated C₁₋₃ alkylgroup, an alkoxy group represented by OR (wherein R is the group definedabove), an aryl group, a substituted aryl group by halogenation, a C₁₋₉alkoxycarbonyl group, a C₁₋₉ alkylcarbonyloxy group, a C₁₋₁₂aryloxycarbonyl group, a C₁₋₁₂ arylcarbonyloxy group and a substitutedderivative thereof, a C₁₋₁₂ arylcarbamoyl group, and a C₁₋₁₂arylcarbonylamino group and a substituted derivative thereof. When thereare plural As, they may be the same or different. The above-mentioned A′is selected from the group consisting of, for example, halogen, a C₁₋₃alkyl group, a halogenated C₁₋₃ alkyl group, a phenyl group and asubstituted phenyl group and when there are plural A's, they may be thesame or different. A substituent on a phenyl ring of the substitutedphenyl group can be, for example, halogen, a C₁₋₃ alkyl group, ahalogenated C₁₋₃ alkyl group or a combination thereof. The t is aninteger from 0 to 4, and the z is an integer from 0 to 3.

Among the repeating units of the polyamide or polyester represented bythe formula (22) above, the repeating unit represented by the generalformula (23) below is preferable.

In the formula (23), A, A′ and Y are those defined by the formula (22),and v is an integer from 0 to 3, preferably is an integer from 0 to 2.Although each of x and y is 0 or 1, not both of them are 0.

On the other hand, a material of the transparent film (b) is notspecifically limited as long as it satisfies the formula (I) in thepresent invention, but it preferably is a polymer with excellenttransparency, and thermoplastic resin that is suitable for achieving thebelow-mentioned stretching treatment and shrinking treatment. Morespecifically, the material of the transparent film (b) may be forexample, acetate resin such as triacetylcellulose (TAC), polyesterresin, polyethersulfone resin, polysulfone resin, polycarbonate resin,polyamide resin, polyimide resin, polyolefin resin, acrylic resin,polynorbornene resin, cellulose resin, polyarylate resin, polystyreneresin, polyvinylalcohol resin, polyvinylchloride resin, polyvinylidenechloride resin, polyacrylic resin, and a mixture thereof. A liquidcrystal polymer is exemplified as well. Moreover, for example, a mixtureof a thermoplasitc resin whose side chain has a substituted orunsubstituted imide group and a thermoplastic resin whose side chain hasa substituted or unsubstituted phenyl group and a nitrile group, whichis described in JP 2001-343529 A (WO01/37007), can be used. A specificexample of the mixed thermoplastic resin is a resin compositioncontaining alternating copolymer containing isobutene and N-methylenemaleimide and a copolymer of acrylonitrile/styrene. Among thesematerials exemplified above, for example, a material which can providerelatively lower birefringent index when used to form a transparent filmis preferred, more specifically, the above-described mixture of athermoplastic resin whose side chain has a substituted or unsubstitutedimide group and a thermoplastic resin whose side chain has a substitutedor unsubstituted phenyl group and a nitrile group is preferable.

Next, a method of manufacturing an optical film of the present inventionis mentioned below. Method of manufacturing an optical film of thepresent invention is not specifically limited as long as it satisfiesthe formula (I), (II) and (III), but for example, first and secondmethods described below can be applied.

The first method of manufacturing an optical film of the presentinvention includes forming of a coating film by applying the material ofthe birefringent layer directly on the transparent substrate that showsuniaxial shrinking property within the plane, and shrinking the coatingfilm by means of shrinkage of the transparent substrate. The coatingfilm is shrunk in accordance with the shrinkage of the transparentsubstrate. In this method, the shrunken transparent substrate becomesthe transparent film (b), and the shrunken coating film becomes thebirefringent layer (a), thereby an optical film of the present inventionhaving the birefringent layer (a) fixed directly on the transparent film(b) is obtained. As described above, the birefringent layer (a) of thepresent invention is laminated directly on the transparent film (b) andall the formulae (I), (II) and (III) are satisfied. The birefringentlayer on the transparent film can be used directly as a viewing anglecompensating film or the like without, for example, being transcribedonto another substrate as in the conventional technique. The substratecan be provided with a shrinking property by a preheating process or thelike.

In this method, the non-liquid crystal polymer such as polyimideinherently shows an optical characteristic of nx=ny>nz, regardless ofthe presence or absence of the orientation of the transparent substrate.Therefore, the coating film formed by the polymer shows opticaluniaxiality, more specifically, shows phase difference only in athickness direction. Since the coating film on the transparent substrateis also shrunk in a thickness direction due to the shrinking property ofthe transparent substrate, the coating film will have an in-planerefractive difference, showing the optical biaxiality (nx>ny>nz).Moreover, for example, by selecting materials of a transparent substrateand a birefringent layer in the manner mentioned above, the formula (I)can be satisfied.

As described above, since the non-liquid crystal polymer possesses anoptical uniaxiality, there is no need of using an orientation of asubstrate. Therefore, both an oriented substrate and a non-orientedsubstrate can be used as the transparent substrate. The substrate canhave a phase difference caused by birefringence, though the phasedifference is not an essential property. An example of a transparentsubstrate that has a phase difference caused by the birefringent effectincludes a stretched film. The stretched film can have a refractiveindex controlled in the thickness direction. The refractive index can becontrolled by, for example, adhering a polymer film to a heat shrinkablefilm, and subsequently heat stretching.

The transparent substrate is preferably stretched in one directionwithin the layer so as to provide a shrinking property in the direction.By previously stretching in this manner, the shrinking force isgenerated in a direction against the stretching direction. Thedifference of the in-plane shrinkage of the transparent substrate isused to provide a difference of the in-plane refractive index to anon-liquid crystal material of the coating film. Specific conditions aredescribed below.

The thickness of the unstretched transparent substrate is notparticularly limited, but it preferably ranges from 10 to 200 μm, morepreferably, from 20 to 150 μm, and particularly preferably, from 30 to100 μm. The draw ratio of stretching is not specifically limited as longas a birefringent layer formed on the above-mentioned stretchedtransparent substrate shows the optical biaxiality (nx>ny>nz).

A method of coating a material of the birefringent layer onto thetransparent substrate is not specifically limited, but the examplesinclude heat-melting and coating the non-liquid crystal polymer, andcoating a polymer solution prepared by dissolving the non-liquid crystalpolymer in a solvent. Among the methods mentioned above, coating thepolymer solution is preferred from its excellent workability.

Polymer density of the polymer solution is not particularly limited, butfor example, it is preferably 5 to 50 parts by weight, or morepreferably, 10 to 40 parts by weight of the polymer material is usedwith respect to 100 parts by weight of the solvent so as to obtain asuitable viscosity for the coating process.

Solvent of the polymer solution is not particularly limited as long asit can dissolve the material of the birefringent layer including thenon-liquid crystal polymer, and can be determined according to the kindof the material. Examples thereof include halogenated hydrocarbons suchas chloroform, dichloromethane, carbon tetrachloride, dichloroethane,tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzeneand orthodichlorobenzene; phenols such as phenol and parachlorophenol;aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzeneand 1,2-dimethoxybenzene; ketone-based solvents such as acetone, methylethyl ketone, methyl isobutyl ketone, cyclohexanone, cyclopentanone,2-pyrrolidone and N-methyl-2-pyrrolidone; ester-based solvents such asethyl acetate and butyl acetate; alcohol-based solvents such astert-butyl alcohol, glycerin, ethylene glycol, triethylene glycol,ethylene glycol monomethyl ether, diethylene glycol dimethyl ether,propylene glycol, dipropylene glycol and 2-methyl-2,4-pentanediol;amide-based solvents such as dimethylformamide and dimethylacetamide;nitrile-based solvents such as acetonitrile and butyronitrile;ether-based solvents such as diethyl ether, dibutyl ether andtetrahydrofuran; or carbon disulfide, ethyl cellosolve or butylcellosolve. These solvents may be used alone or in combination of two ormore.

In the polymer solution, various known additives such as a stabilizer, aplasticizer, metal and the like further may be blended as necessary.

Moreover, the polymer solution may contain other resins as long as theorientation of the material does not drop considerably. Such resins canbe, for example, resins for general purpose use, engineering plastics,thermoplastic resins and thermosetting resins.

The resins for general purpose use can be, for example, polyethylene(PE), polypropylene (PP), polystyrene (PS), polymethyl methacrylate(PMMA), an ABS resin, an AS resin or the like. The engineering plasticscan be, for example, polyacetate (POM), polycarbonate (PC), polyamide(PA: nylon), polyethylene terephthalate (PET), polybutyleneterephthalate (PBT) or the like. The thermoplastic resins can be, forexample, polyphenylene sulfide (PPS), polyethersulfone (PES), polyketone(PK), polyimide (PI), polycyclohexanedimethanol terephthalate (PCT),polyarylate (PAR), liquid crystal polymers (LCP) or the like. Thethermosetting resins can be, for example, epoxy resins, phenolic novolacresins or the like.

When the above-described other resins are blended in the polymersolution as mentioned above, the blend amount ranges, for example, from0 wt % to 50 wt %, preferably from 0 wt % to 30 wt %, with respect tothe polymer material.

Examples of the method of coating the polymer solution include spincoating, roller coating, flow coating, printing, dip coating, filmflow-expanding, bar coating, gravure printing, or the like. In thecoating, a method of superimposing a polymer layer can be adopted, asnecessary.

Furthermore, the transparent substrate is shrunk by heating a coatingfilm on the transparent substrate. In accordance with the shrinkage ofthe transparent substrate, this coating film is shrunk, thereby formingthe birefringent layer (a). Though conditions of the heat processing arenot limited specifically and can be determined according to the kinds orthe like of the materials of the transparent substrate, for example, thetemperature preferably ranges from 25 to 300° C., more preferably, from50 to 200° C., and particularly preferably, from 60 to 180° C.

After the heating, the solvent of the polymer solution remaining in thebirefringent layer (a) may change optical characteristics of the opticalfilm over time in proportion to the residual amount. Therefore, theamount of the remaining solvent is preferably 5% or the less, and morepreferably 2% or the less, and further preferably 0.2% or less.

The second method of manufacturing the optical film of the presentinvention includes forming a coating film by directly coating thematerial of the birefringent layer on the transparent substrate,thereafter stretching the transparent substrate and the coating filmtogether. In this method, the stretched transparent substrate becomesthe transparent film (b), and similarly, the stretched coating filmbecomes the birefringent layer (a). Therefore, the optical film of thepresent invention has the birefringent layer (a) fixed directly on thetransparent film (b). The optical film obtained by the second method hasan effect similar to the optical film obtained by the first methodmentioned above. In the second manufacturing method, the process ofcoating the material of the birefringent layer (a) may be the same asthat in the first manufacturing method.

In this method, similar to the first method of manufacturing, thenon-liquid crystal polymer such as polyimide shows an opticalcharacteristic of nx=ny>nz, regardless of the presence or absence of theorientation in the transparent substrate. Therefore, the coating filmformed by the polymer shows optical uniaxiality. In addition, bystretching the laminate of the transparent substrate and the coatingfilm in one of the directions in the plane, the coating film will have arefractive difference in the plane, thereby showing the opticalbiaxiality (nx>ny>nz).

Methods of stretching the laminate of the transparent substrate and thecoating film are not particularly limited, but examples includestretching the film uniaxially in the longitudinal direction (free-endlongitudinal stretching), stretching the film uniaxially in thetransverse direction while the film is fixed in the longitudinaldirection (fixed-end transverse stretching), and stretching the filmboth in the longitudinal and transverse directions (sequential orconcurrent biaxial stretching).

Though the stretching of the laminate may be carried out, for example,by stretching both the transparent substrate and the coating filmtogether, it is preferable, for example, that only the transparentsubstrate is stretched, for the following reason. When stretching thetransparent substrate solely, the coating film on the transparentsubstrate is stretched indirectly by a tension generated in thetransparent substrate as a result of this stretching. In general, a moreuniform stretch can be obtained when stretching a single layer thanstretching a laminate. Therefore, by uniformly stretching thetransparent substrate, the coating film on the transparent substrate canbe stretched also uniformly.

Conditions of stretching are not particularly limited but can bedetermined according to the kinds of the materials of the transparentsubstrate, the birefringent layer or the like. Specifically, the drawratio of stretching is greater than 1 and not greater than 5, morepreferably, greater than 1 and not greater than 4, and particularlypreferably, greater than 1 and not greater than 3.

When manufacturing an optical film by the second manufacturing method,the formula (I) can be satisfied by, for example, selecting materialsfor the transparent substrate and the birefringent layer in theabove-described manner,.

A method for manufacturing an optical film of the present inventionother than the first and second methods mentioned above includes formingthe material of the birefringent layer (a) as a thin film on thetransparent substrate being under a stress in one direction within theplane.

Alternatively, for example, the materials are formed into thin films onthe transparent film (b) by blowing air or the like in one direction, orthe materials are coated on the transparent film (b) provided with theanisotropy.

It is preferable that the optical film of the present invention furtherincludes at least one of an adhesive layer and a pressure-sensitiveadhesive layer in order to facilitate adhesion of the optical film ofthe present invention with the other members such as the other opticallayers and a liquid crystal cell, and also to prevent the optical filmof the present invention from peeling off. Accordingly, the adhesivelayer and the pressure-sensitive adhesive layer are laminated preferablyon the outermost surface of the optical film. More specifically, thelayers may be laminated on one or both outermost surface(s) of theoptical film.

Though there is no specific limitation on the material of the adhesivelayer, examples of the materials used for the adhesive layer include arubber-based pressure sensitive adhesive and a pressure-sensitiveadhesive based on a polymer such as an acrylic substances, vinylalcohol, silicone, polyester, polyurethane and polyether. Fine particlescan also be blended into those materials in order to form an adhesivelayer having a light diffusion property. Among them, materials havingexcellent moisture-absorption and heat resistance are preferred. Aliquid crystal display manufactured by using the materials will beexcellent in quality and durability, since disadvantages such as foamingand peeling caused by moisture absorption, degradation in the opticalcharacteristics and warping of the liquid crystal cell that are causedby a difference in the thermal expansion, can be prevented.

The optical film of the present invention can be used solely asmentioned above, or it can be combined with other optical members asrequired so as to form a laminate for various optical uses. Morespecifically, the optical film can be used for an optical compensatingmember, in particular, for a viewing angle compensating member. Theoptical member to be combined with the optical film is not particularlylimited, but an example thereof is a polarizer, explained below indetail.

A laminated polarizing plate of the present invention characterized inthat it includes an optical film and a polarizer, and the optical filmis provided according to the present invention.

The configuration of the polarizing plate is not limited particularly aslong as it includes an optical film of the present invention, but theexamples are illustrated in FIGS. 2 and 3. FIGS. 2 and 3 arecross-sectional views respectively showing the examples of the laminatedpolarizing plate of the present invention, with the same parts assignedwith the same reference numerals. Here, the polarizing plate of thepresent invention is not limited to the configuration mentioned below,and may further include other optical members or the like.

The laminated polarizing plate 20 shown in FIG. 2, includes the opticalfilm 1 of the present invention, the polarizer 2, and a two transparentprotective layers 3, wherein the transparent protective layers 3 arelaminated on both sides of the polarizer 2, and the optical film 1 isfurther laminated respectively on one of the transparent protectivelayers 3. Since the optical film 1 is a laminate of the birefringentlayer (a) and the transparent film (b) as mentioned above, eithersurface of the optical film 1 can face the transparent protective film3.

The transparent protective films 3 can be laminated on one or bothsurface(s) of the polarizer 2. When the transparent protective films 3are laminated on both surfaces of the polarizer 2, they may be the sameor different.

The laminated polarizing plate 30 in FIG. 3 includes the optical film 1of the present invention, the polarizer 2 and the transparent protectivefilms 3, and the optical film 1 and the transparent protective films 3are laminated on the respective surfaces of the polarizer 2.

As mentioned above, since the optical film 1 is a laminate of thebirefringent layer (a) and the transparent film (b), either surface ofthe optical film 1 can face the polarizer 2. Preferably, the opticalfilm is arranged so that the transparent film (b) of the optical film 1faces the polarizer 2. For example, the transparent film (b) of theoptical film 1 can be used also as a transparent protective layer in alaminated polarizing plate. More specifically, instead of laminatingtransparent protective layers on both surfaces of the polarizer, atransparent protective layer is laminated on one surface of thepolarizer, and the optical film is laminated on the other surface of thepolarizer so that the transparent film will be faced the polarizer.Thereby, the transparent film can also function as a transparentprotective layer on the other surface of the polarizer. As a result, thethickness of the polarizing plate can be decreased further.

The polarizer is not particularly limited, but can be a film, forexample, prepared by being dyed by adsorbing a dichroic material such asiodine or a dichroic dye, followed by cross-linking, stretching anddrying. Among them, films that can penetrate linearly polarized lightwhen natural light is entered, more specifically, films having excellentlight transmittance and polarization degree are preferable. Examples ofthe polymer film in which the dichroic material is to be adsorbedinclude hydrophilic polymer films such as polyvinyl alcohol (PVA)-basedfilms, partially-formalized PVA-based films, partially-saponified filmsbased on ethylene-vinyl acetate copolymer and cellulose-based films.Other than the above, a polyene oriented film such as dehydrated PVA anddehydrochlorinated polyvinyl chloride can be used, for example. Amongthem, the PVA-based film is preferable. In addition, the thickness ofthe polarizing film generally ranges from 1 to 80 μm, though it is notlimited to this.

The protective layer is not particularly limited but can be aconventionally known transparent film. For example, transparentprotective films having excellent transparency, mechanical strength,thermal stability, moisture shielding property and isotropism arepreferable. Specific examples of materials for such a transparentprotective layer can include cellulose-based resins such as cellulosetriacetate (TAC), and transparent resins based on polyester,polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone,polystyrene, polynorbornene, polyolefin, acrylic substances, acetate andthe like. Thermosetting resins or ultraviolet-curing resins based on theacrylic substances, urethane, acrylic urethane, epoxy, silicones and thelike can be used as well. Among them, a TAC film having a surfacesaponified with alkali or the like is preferable in light of thepolarization property and durability.

Another example of the polymer film is described in JP 2001-343529 A (WO01/37007). The polymer material used can be a resin compositioncontaining a thermoplastic resin whose side chain has a substituted orunsubtituted imido group and a thermoplastic resin whose side chain hasa substituted or unsubtituted phenyl group and nitrile group, forexample, a resin composition containing an alternating copolymer ofisobutene and N-methylene maleimide and an acrylonitrile-styrenecopolymer. Alternatively, the polymer film may be formed by extrudingthe resin composition.

It is preferable that the protective layer is colorless. Morespecifically, a retardation value (Rth) of the film in its thicknessdirection as represented by the equation below preferably ranges from−90 nm to +75 nm, more preferably ranges from −80 nm to +60 nm, andparticularly preferably ranges from −70 nm to +45 nm. When theretardation value is within the range of −90 nm to +75 nm, coloring(optical coloring) of the polarizing plate, which is caused by theprotective film, can be solved sufficiently. In the equation below, nx,ny and nz are equivalent to those described above, and d indicates thethickness of this film.Rth={[(nx+ny)/2]−nz}×d

The transparent protective layer may further have an opticallycompensating function. As such a transparent protective layer having theoptically compensating function, it is possible to use, for example, aknown layer used for preventing coloring caused by changes in a visibleangle based on retardation in a liquid crystal cell or for widening apreferable viewing angle. Specific examples include various filmsobtained by stretching the above-described transparent resins uniaxiallyor biaxially, an oriented film of a liquid crystal polymer or the like,and a laminate obtained by providing an oriented layer of a liquidcrystal polymer on a transparent base. Among the above, the orientedfilm of a liquid crystal polymer is preferable because a wide viewingangle with excellent visibility can be achieved. Particularly preferableis an optically compensating retardation plate obtained by supporting anoptically compensating layer with the above-mentioned triacetylcellulosefilm or the like, where the optically compensating layer is made of anincline-oriented layer of a discotic or nematic liquid crystal polymer.This optically compensating retardation plate can be a commerciallyavailable product, for example, “WV film” manufactured by Fuji PhotoFilm Co., Ltd. Alternatively, the optically compensating retardationplate can be prepared by laminating two or more layers of the opticalretardation film and a film support of triacetylcellulose film or thelike so as to control optical characteristics such as retardation.

The thickness of the transparent protective layer is not particularlylimited but can be determined suitably according to retardation or aprotection strength. In general, the thickness is not greater than 500μm, preferably ranges from 5 to 300 μm, and more preferably ranges from5 to 150 μm.

The transparent protective layer can be formed suitably by a knownmethod such as a method of coating a polarizing film with theabove-mentioned various transparent resins or a method of laminating thetransparent resin film, the optically compensating retardation plate orthe like on the polarizing film, or can be a commercially availableproduct.

The transparent protective layer may be further subjected to, forexample, a hard coating treatment, an antireflection treatment,treatments for anti-sticking, diffusion and anti-glaring and the like.The hard coating treatment aims to prevent scratches on the surfaces ofthe polarizing plate, and is a treatment of, for example, providing ahardened coating film that is formed of a curable resin and hasexcellent hardness and smoothness onto a surface of the transparentprotective film. The curable resin can be, for example,ultraviolet-curing resins of silicone base, urethane base, acrylic, andepoxy base. The treatment can be carried out by a known method. Theanti-sticking treatment aims to prevent adjacent layers from sticking toeach other. The antireflection treatment aims to prevent reflection ofexternal light on the surface of the polarizing plate, and can becarried out by forming a known antireflection film or the like.

The anti-glare treatment aims to prevent hindering visibility of lighttransmitted through the polarizing plate due to the reflection ofexternal light on the polarizing plate surface. The anti-glare treatmentcan be carried out, for example, by providing microscopic asperities ona surface of a transparent protective film by a known method. Suchmicroscopic asperities can be provided, for example, by roughening thesurface by sand-blasting or embossing, or by blending transparent fineparticles in the above-described transparent resin when forming thetransparent protective layer.

The above-described transparent fine particles may be silica, alumina,titania, zirconia, stannic oxide, indium oxide, cadmium oxide, antimonyoxide or the like. Other than the above, inorganic fine particles havingan electrical conductivity or organic fine particles comprising, forexample, crosslinked or uncrosslinked polymer particles can be used aswell. The average particle diameter of the transparent fine particlesranges, for example, from 0.5 to 20 μm, though there is no specificlimitation. In general, a blend ratio of the transparent fine particlespreferably ranges from 2 to 70 parts by weight, and more preferablyranges from 5 to 50 parts by weight with respect to 100 parts by weightof the above-described transparent resin, though there is no specificlimitation.

An anti-glare layer in which the transparent fine particles are blendedcan be used as the transparent protective layer itself or provided as acoating layer applied onto the transparent protective layer surface.Furthermore, the anti-glare layer also can function as a diffusion layerto diffuse light transmitted through the polarizing plate in order towiden the viewing angle (i.e., visually-compensating function).

The antireflection layer, the anti-sticking layer, the diffusion layerand the anti-glare layer mentioned above can be laminated on thepolarizing plate, as an sheet of optical layers comprising these layers,separately from the transparent protective layer.

Method for laminating each members (an optical film, a polarizer, atransparent protective layer, etc) is not particularly limited and canbe a conventional method. Generally, the above-mentioned adhesive andsticking agent can be used, and the kind thereof can be determinedsuitably depending on materials of the birefringent layer and thepolarizing plate. The adhesive can be, for example, a polymer adhesivebased on acrylic substances, vinyl alcohol, silicone, polyester,polyurethane or polyether, or a rubber-based adhesive. It also ispossible to use an adhesive or rubber adhesive containing awater-soluble cross-linking agent of vinyl alcohol-based polymers suchas glutaraldehyde, melamine and oxalic acid. The sticking agent and theadhesive mentioned above do not peel off easily even when being exposedto moisture or heat, for example, and have excellent light transmittanceand polarization degree. More specifically, these sticking agent andadhesive preferably are PVA-based adhesives when the polarizing plate isa PVA-based film, in light of stability of adhering treatment. Thesesticking agent and adhesive may be applied directly to surfaces of thepolarizing plate and the transparent protective layer, or a layer of atape or a sheet formed of the sticking agent or adhesive may be arrangedon the surfaces thereof. Further, when these sticking agent and adhesiveare prepared as an aqueous solution, for example, other additives or acatalyst such as an acid catalyst may be blended as necessary. In thecase of applying the adhesive, other additives or a catalyst such as anacid catalyst further may be blended in the aqueous solution of theadhesive. The thickness of the adhesive layer is not particularlylimited but may be, for example, 1 to 500 nm, preferably 10 to 300 nm,and more preferably 20 to 100 nm. It is possible to adopt a known methodof using an adhesive such as an acrylic polymer or a vinyl alcohol-basedpolymer without any particular limitations. Moreover, in order to form apolarizing plate that does not peel off easily by moisture or heat andhas excellent light transmittance and polarization degree, the adhesivepreferably further contains a water-soluble cross-linking agent ofPVA-based polymers such as glutaraldehyde, melamine and oxalic acid.These adhesives can be used, for example, by applying its aqueoussolution to the surface of each member mentioned above, followed bydrying. In the above aqueous solution, other additives or a catalystsuch as an acid catalyst may be blended as necessary. Among these, theadhesive preferably is a PVA-based adhesive because an excellentadhesiveness to a PVA film can be achieved.

The optical film of the present invention can be used in combinationwith, for example, various retardation plates, diffusion-control films,and brightness-enhancement films. The retardation film can be preparedby, for example, stretching a polymer uniaxially or biaxially,subjecting a polymer to Z-axis orientation, or coating a liquid crystalpolymer on a base. The diffusion-control films can use diffusion,scattering, and refraction for controlling viewing angles, or forcontrolling glaring and scattered light that will affect definition. Thebrightness-enhancement film may include a λ/4 wavelength plate (a λ/4plate) and a selective reflector of a cholesteric liquid crystal, and ascattering film using an anisotropic scatter depending on thepolarization direction. The optical film can be, for example, combinedwith a wire grid polarizer.

In use, the laminated polarizing plate of the present invention canfurther contain other optical layers in addition to the optical films ofthe present invention. Examples of the optical layers includeconventionally known optical layers used for forming liquid crystaldisplays or the like, such as below-mentioned polarizing plates,reflectors, semitransparent reflectors, and brightness-enhancementfilms. These optical layers can be used alone, or at least two kinds oflayers can be used together. A laminated polarizing plate furtherincluding the optical layer is used preferably as an integratedpolarizing plate having an optical compensation function, and forexample, it is suitably applied to various image displays, for example,by being arranged on a surface of a liquid crystal cell.

The integrated polarizing plate will be described below in detail.

First, an example of a reflective polarizing plate or a semitransparentreflective polarizing plate is described. The reflective polarizingplate is prepared by laminating a reflector additionally on thelaminated polarizing plates of the present invention, and asemitransparent reflective polarizing plate is prepared by laminating asemitransparent reflector additionally on the laminated polarizingplates of the present invention.

In general, the reflective polarizing plate is arranged on a backside ofa liquid crystal cell in order to make a liquid crystal display toreflect incident light from a visible side (display side) of areflective type liquid crystal display. The reflective polarizing platehas some merits, for example, assembling of light sources such asbacklight can be omitted, and the liquid crystal display can be thinnedfurther.

The reflective polarizing plate can be formed in any known manner suchas forming a reflector of metal or the like on one surface of thepolarizing plate that exhibits an elastic modulus. More specifically,for example, a transparent protective layer of the polarizing plate isprepared by matting one surface (surface to be exposed) as required. Onthis surface, a foil comprising a reflective metal such as aluminum or adeposition film is applied to form a reflector.

An additional example of a reflective polarizing plate includes thetransparent protective layer that has a surface with microscopicasperities formed by blending fine particles in transparent resins asdescribed above. The reflective polarizing plate also includes areflecting layer corresponding to the microscopic asperities. Thereflecting layer having a microscopic asperity surface diffuses incidentlight irregularly so that directivity and glare can be prevented andirregularity in color tones can be controlled. The reflector can beformed as the foil or the deposition film comprising a metal, byattaching a metal directly on a surface of the transparent protectivelayer with microscopic asperities in any conventional and appropriatemethods including deposition such as vacuum deposition, and plating suchas ion plating and sputtering.

The above-mentioned reflective polarizing plate is manufactured bydirectly forming the reflector on a transparent protective layer of thepolarizing plate. Alternatively, the reflector can be used as areflecting sheet formed by providing a reflecting layer onto a properfilm similar to the transparent protective film. Since a typicalreflecting layer of a reflector is made of a metal, it is preferablyused in a state coated with the film, a polarizing plate or the like inorder to prevent a reduction of the reflection rate due to oxidation,and by extension, to maintain the initial reflection rate for a longperiod, and to prevent formation of an additional transparent protectivefilm.

The semitransparent polarizing plate is provided by replacing thereflector in the above-mentioned reflective polarizing plate by atransflector, and it is exemplified by a half mirror that reflects andtransmits light at the reflector.

In general, such a semitransparent polarizing plate is arranged on abackside of a liquid crystal cell, and can be used for the following: aliquid crystal display comprising the semitransparent polarizing plate,wherein incident light from the visible side (display side) is reflectedto display an image when a liquid crystal display is used in arelatively bright atmosphere, while in a relatively dark atmosphere, animage is displayed by using a built-in light source such as a backlighton the backside of the semitransparent polarizing plate. In other words,the semitransparent polarizing plate can be used to form a liquidcrystal display that can save energy for a light source such as abacklight under a bright atmosphere, while a built-in light source canbe used under a relatively dark atmosphere.

Next, an example of a polarizing plate comprising abrightness-enhancement film further laminated on a laminated polarizingplate of the present invention will be described.

The brightness-enhancement film is not particularly limited, but asuitable example of the brightness-enhancement film is selected from amultilayer thin film of a dielectric or a multilayer lamination of thinfilms with varied refraction aeolotropy (e.g., trade name: D-BEFmanufactured by 3M Co.) that transmits linearly polarized light having apredetermined polarization axis while reflecting other light, and acholesteric liquid crystal layer, more specifically, an oriented film ofa cholesteric liquid crystal polymer or an oriented liquid crystal layerfixed onto a supportive substrate (e.g., trade name: PCF 350manufactured by Nitto Denko Corporation, or trade name: Transmaxmanufactured by Merck and Co., Inc.) that reflects either clockwise orcounterclockwise circularly polarized light while transmitting otherlight.

Above stated polarizing plate of the present invention may be an opticalmember including, for example, a laminated polarizing plate of thepresent invention and at least two optical layers laminated furtherthereon.

An optical member comprising a laminate of at least two optical layerscan be formed by a method of laminating layers separately in a certainorder for manufacturing a liquid crystal display or the like. Since anoptical member that has been laminated previously has excellentstability in quality and assembling operability, efficiency inmanufacturing a liquid crystal display can be improved. Any appropriateadhesives such as a pressure-sensitive adhesive layer can be used forthe lamination.

It is preferable that the above-described various polarizing platesfurther comprise pressure-sensitive adhesive layers and adhesive layers,so that lamination of the polarizing plates onto the other member suchas a liquid crystal cell will be facilitated. The pressure-sensitiveadhesive layers and adhesive layers can be arranged on one or bothsurface of the polarizing plates. Materials of the pressure-sensitiveadhesive layers are not particularly limited, and conventionally knownmaterials such as acrylic polymers can be used. More specifically,materials for the pressure-sensitive adhesive layer are particularlypreferred to have low moisture absorption and excellent heat resistance,in order to prevent foaming and exfoliation caused by moistureabsorption, and optical characteristics deterioration and warp of aliquid crystal cell caused by the thermal expansion difference,accordingly to manufacture a liquid crystal display with high qualityand excellent durability. The pressure-sensitive adhesive layer maycontain fine particles for diffusing light. The pressure-sensitiveadhesive layer can be formed on the surface of the polarizing plate, forexample, by adding the solution or molten liquid of various stickingmaterials directly on a predetermined face of the polarizing plate bythe expanding method such as flow-expanding and coating. Thepressure-sensitive adhesive layer on the surface of the polarizing platemay be obtained also by forming a pressure-sensitive adhesive layer on abelow-mentioned separator in the same manner as described above,subsequently removing and fixing it onto a predetermined surface of thepolarizing plate. Here, the pressure-sensitive adhesive layer can beformed on any surface of the polarizing plate. Specifically for example,it can be formed on the exposed surface of the retardation plate in thepolarizing plate.

When a surface of a pressure-sensitive adhesive layer on a surface ofthe polarizing plate is exposed, the pressure-sensitive adhesive layeris preferably covered with a separator until the time thepressure-sensitive adhesive layer is used so that contamination will beprevented. The separator can be formed by coating, on an appropriatefilm such as the transparent protective film, a layer including at leastone layer of a peeling agent containing silicone, long-chain alkyl,fluorine, molybdenum sulfide or the like as required.

The pressure-sensitive adhesive layer or the like may be, for example, asingle layer or a laminate. For the laminate, for example, layersdifferent from each other in the compositions and in the types can becombined. In a case of arranging on both surfaces of the polarizingplate, the pressure-sensitive layers can be the same or can be differentfrom each other in the compositions and the types.

The thickness of the pressure-sensitive adhesive layer can be determinedaccording to the configuration of the polarizing plate or the like, andgenerally, it ranges from 1 to 500 μm.

The sticking agent forming the pressure-sensitive adhesive layer hasexcellent optical transparency and sticking properties includingappropriate wettability, cohesiveness, and stickiness. For example,sticking agent can be prepared by processing a polymer such as anacrylic polymer, a silicone-based polymer, polyester, polyurethane,polyether and polymers based on a synthetic rubber, as a base polymer,as required.

The sticking property of the pressure-sensitive adhesive layer can becontrolled by a conventionally known method, for example, by controllingthe cross-linking degree and molecular weight depending on thecomposition, the molecular weight, the cross-linking form, the contentof the cross-linking functional group and the rate for blending thecross-linking agent for the base polymer forming the pressure-sensitiveadhesive layer.

The above-described layers of the present invention, such as an opticalfilm, a laminated polarizing plate, polarizing films for forming variousoptical members (various polarizing plates prepared by laminatingoptical layers), a transparent protective layer, an optical layer, and apressure-sensitive adhesive layer can have ultraviolet absorption poweras a result of treatment with an ultraviolet absorber such as ansalicylate compound, a benzophene-based compound, a benzotriazolecompound, a cyanoacrylate compound, and a nickel complex salt compound.

As mentioned above, an optical film and a laminated polarizing plate ofthe present invention is preferably used for manufacturing variousdevices such as liquid crystal displays. For example, they are arrangedon one or both surfaces of a liquid crystal cell to form a liquidcrystal panel so as to provide various types of liquid crystal displayssuch as reflective, semitransparent, transparent-reflective liquidcrystal displays or the like.

The kind of the liquid crystal cell forming a liquid crystal display maybe selected arbitrarily, and can be any type of liquid crystal cellssuch as an active-matrix driving type represented by a thin-filmtransistor type, or a simple-matrix driving type represented by atwisted nematic type or a super twisted nematic type. Among them, sincethe optical film and the polarizing plate of the present invention areparticularly excellent in the optical compensation for a VA (verticallyaligned) cell, they are suitably used for viewing angle compensatingfilms for VA-mode liquid crystal displays.

Generally, the liquid crystal cell has a configuration that liquidcrystal is injected between liquid crystal cell substrates that arearranged facing each other. The liquid crystal cell substrate is notparticularly limited, and the examples include a glass substrate and aplastic substrate. Moreover, materials of the plastic substrate are notlimited specifically, and conventionally known materials can be used.

When polarizing plates or optical members are arranged on both surfacesof a liquid crystal panel, the kinds of polarizing plates or the opticalmembers on the surfaces can be the same or different. Moreover, forforming a liquid crystal display, an appropriate member such as a prismarray sheet, a lens array sheet, an optical diffuser and a backlight canbe arranged by one or plural layer(s) at proper positions as required.

Furthermore, a liquid crystal display of the present invention is notlimited particularly, except that it includes a liquid crystal panel ofthe present invention. When the liquid crystal display includes a lightsource, the light source is not particularly limited, but a flat lightsource emitting polarized light is preferred since it enables effectiveuse of light energy.

The cross-sectional view in FIG. 4 shows one example of a liquid crystalpanel of the present invention. As shown in the figure, a liquid crystalpanel 40 includes a liquid crystal cell 21, an optical film 1, apolarizer 2 and a transparent protective layer 3. The optical film 1 islaminated on one surface of the liquid crystal cell 21, and thepolarizer 2 and the transparent protective layer 3 are laminated in thisorder on the other surface of the optical film 1. The liquid crystalcell includes two liquid crystal cell substrates and liquid crystal thatis held between the two liquid crystal cell substrates (not shown in thefigure). As mentioned above, the optical film 1 is a laminate of abirefringent layer (a) and a transparent film (b), the birefringentlayer (a) faces the liquid crystal cell 21 and the transparent film (b)faces the polarizer 2.

In the liquid crystal display of the present invention, a diffusionplate, an anti-glare layer, an antireflection film, a protective layeror a protective plate further may be disposed on the optical film (apolarizing plate) on the viewing side. Alternatively, a retardationplate for compensation or the like can be arranged between a liquidcrystal cell and a polarizing plate in a liquid crystal panel, asrequired.

An optical film and a laminated polarizing plate of the presentinvention can be used not only in the above-described liquid crystaldisplay but also in, for example, self-light-emitting displays such asan organic electroluminescence (EL) display, a PDP, and a FED. Whenusing the optical film and the laminated polarizing plate of the presentinvention as antireflective filters in self-light-emitting flatdisplays, circularly polarized light can be obtained, for example, bysetting an in-plane retardation value (Δnd) of a birefringent opticalfilm of the present invention to be λ/4.

The following is a specific description of an electroluminescence (EL)display including a polarizing plate of the present invention. The ELdisplay of the present invention is a display including the optical filmor the laminated polarizing plate of the present invention and can beeither an organic EL display or an inorganic EL display.

In recent years, in an EL display as well, use of optical films such asa polarizer and a polarizing plate together with a λ/4 plate have beenproposed for preventing reflection from an electrode in a blackcondition. An optical film and a laminated polarizing plate of thepresent invention are exceedingly useful, particularly for example, whenany of linearly polarized light, circularly polarized light orelliptically polarized light is emitting from an EL layer, and whenobliquely-emitted light among natural light emitted in the frontdirection is partly polarized.

A typical organic EL display is described below in detail. The organicEL display generally includes a light emitter (an organic EL lightemitter) formed by laminating a transparent electrode, an organiclight-emitting layer and a metal electrode in this order on atransparent substrate. The organic light-emitting layer is a laminate ofvarious kinds of organic thin films. Examples of the combinationinclude: a laminate of a hole-injecting layer including triphenylaminederivative or the like and a light-emitting layer comprising afluorescent organic solid body such as anthracene; a laminate of thelight-emitting layer and an electron-injective layer comprising perylenederivative or the like; and a laminate of the hole-injecting layer, thelight-emitting layer and the electron-injective layer.

The organic EL display emits light in the following principle. That is,holes and electrons are injected into the organic light-emitting layerby applying voltage to the positive and negative electrodes, and energygenerated by recombination of the holes and the electrons excitesfluorescent substances, and the thus excited fluorescent substances emitlight when recovering to the ground state. The mechanism of therecombination of the holes and electrons is similar to that of a generaldiode, and a current and emission intensity show strong nonlinearityinvolving commutation with respect to the applied voltage.

In the organic EL display, at least one of the electrodes must betransparent so that the light emitted in the organic light-emittinglayer can be taken out. Therefore, a transparent electrode formed of atransparent conductor such as indium tin oxide (ITO) is generally usedas a positive electrode. On the other hand, in order to facilitateelectron injection and increase the light emission efficiency, it isimportant to use a substance with a small work function for a negativeelectrode, and thus a metal electrode such as Mg—Ag and Al—Li is used ingeneral.

In an organic EL display having the above-mentioned configuration, theorganic light-emitting layer is preferably formed of an exceedingly thinfilm, for example, with a thickness of about 10 nm, so that the organiclight-emitting layer will penetrate light almost perfectly, just as thetransparent electrode does. Therefore, a light beam, which entersthrough the surface of the transparent substrate and passes through thetransparent electrode and the organic light-emitting layer so as to bereflected on the metal electrode, is emitted again toward the surface ofthe transparent substrate during a non-emission period. As a result, ascreen of the organic EL display appears like a mirror when visuallyidentified from outside.

An organic EL display of the present invention, for example, includesthe organic EL light-emitter that has a transparent electrode formed onthe surface side of the organic light-emitting layer and a metalelectrode formed on the backside of the same organic light-emittinglayer. In the organic EL display, it is preferable that an optical film(e.g., a polarizing plate) of the present invention is arranged on thesurface of the transparent electrode, and further preferably, a λ/4plate is arranged between a polarizing plate and an EL element. Byarranging the optical film of the present invention in this manner, theorganic EL display will have an effect of preventing the reflection ofexternal light and enable to improve visual recognition. It ispreferable that a retardation plate is arranged between the transparentelectrode and the optical film.

The retardation plate and the optical film (a polarizing plate or thelike) have, for example, a polarizing effect against light that entersfrom outside and is reflected by the metal electrode, and due to thepolarizing effect, a mirror-like surface of the metal electrode isprevented from being recognized visually from outside. In particular,when a 1/4 wavelength plate is used as a retardation plate andfurthermore, the angle between the polarizing directions of thepolarizing plate and the retardation plate is set to be π/4, themirror-like surface of the metal electrode can be fully shielded. Morespecifically, only a linearly polarized component of the external lightentering the organic EL display penetrates by means of the polarizingplate. The linearly polarized light is generally converted intoelliptically polarized light by the retardation plate, and particularly,it is converted into circularly polarized light when the retardationplate is a 1/4 wavelength plate and the angle between the polarizingdirections of the polarizing plate and the retardation is π/4.

The circularly polarized light penetrates, for example, a transparentsubstrate, a transparent electrode and an organic thin film, reflectedby the metal electrode, thereafter penetrates the organic thin film, thetransparent electrode and the transparent substrate again, and it isconverted into the linearly polarized light again at the retardationplate. This linearly polarized light cannot penetrate the polarizingplate because its polarizing direction is orthogonal to that of thepolarizing plate, thereby, the mirror surface of the metal electrode canbe fully shielded, as mentioned above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples of the present invention and Comparative examples will bedescribed further below in detail, though the present invention is notlimited to the Examples. The characteristics of the optical film weremeasured in the following manner.

(Retardation Value Δnd, Precision in Orientation Axis)

A retardation value and a precision in orientation axis were measuredwith a retardation analyzer (trade name: KOBRA-21ADH manufactured by OjiScientific Instruments).

(Refractive Index)

A refractive index at a wavelength of λ=590 was measured withKOBRA-21ADH (trade name) manufactured by Oji Scientific Instruments.

(Thickness)

A thickness is measured with DIGITAL MICROMETER-K-351C manufactured byAnritsu.

EXAMPLE 1

Polyimide having molecular weight (Mw) of 70,000, which is representedby the below-mentioned figure (6), was synthesized from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB), and dissolved incyclohexanone so as to prepare a 15 wt % polyimide solution. Regardingthe preparation of polyimide or the like, description of “Polymer” 40(1999) 4571-4583, F. Li et al. was referenced to. A triacetylcellulose(TAC) film with a thickness of 80 μm was stretched 1.3 times itsoriginal length in the transverse direction by fixed-end transversestretching at 175° C., thereby a stretched TAC film with a thickness of75 μm was obtained. The thus stretched TAC film was coated with thepolyimide solution, and dried for 10 minutes at 100° C., so as to obtainan optical film. The optical film includes a completely transparent andflat stretched TAC film with a thickness of 75 μm and Δn(b) ofapproximately 0.0006 (a transparent film (b)), and a polyimide film witha thickness of 6 μm and Δn(a) of approximately 0.04 (the birefringentlayer (a)), being laminated on the transparent film (b). This opticalfilm included a birefringent layer having an optical characteristic ofnx>ny>nz.

EXAMPLE 2

Polyetherketone (Mw=500,000) represented by the below-mentioned figure(18) was dissolved in methyl isobutyl ketone so as to prepare a 20 wt %varnish. This vanish was coated on a stretched TAC film as in Example 1,and dried for 10 minutes at 100° C. so as to obtain an optical film. Theoptical film included a completely transparent and flat stretched TACfilm with a thickness of 75 μm and a Δn(b) of approximately 0.0006 (atransparent film (b)), and a polyether ketone film with a thickness of10 μm and a Δn(a) of approximately 0.02 (a birefringent layer (a)),laminated on the transparent film (b). This optical film included abirefringent layer having an optical characteristic of nx>ny>nz.

EXAMPLE 3

Polyimide (Mw=30,000) was synthesized from4,4′-bis(3,4-dicarboxyphenyl)-2,2-diphenylpropane dianhydride and2,2′-dichrolo-4,4′-diaminobiphenyl, and dissolved in cyclopentanone soas to prepare a 20 wt % polyimide solution. This solution was coated onan unstretched TAC film with a thickness of 80 μm, dried for 5 minutesat 130° C., and stretched by 10% its original length by longitudinaluniaxial stretching at 150° C. so as to obtain an optical film. Theoptical film included a completely transparent and flat TAC film with athickness of 80 μm and a Δn(b) of approximately 0.0006 (a transparentfilm (b)), and a polyimide film with a thickness of 5 μm and a Δn(a) ofapproximately 0.025 (a birefringent layer (a)), being laminated on thetransparent film (b). This optical film included a birefringent layerhaving an optical characteristic of nx>ny>nz.

EXAMPLE 4

Polyimide (Mw=100,000) was synthesized from2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride and2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, and dissolved incyclohexanone so as to prepare a 15 wt % polyimide solution. Thissolution was coated on an unstretched TAC film with a thickness of 80μm, dried for 5 minutes at 130° C. and stretched by 10% its originallength by longitudinal uniaxial stretching at 150° C. so as to obtain anoptical film. The optical film included a completely transparent andflat TAC film with a thickness of 80 μm and a Δn(b) of approximately0.0006 (a transparent film (b)), and a polyimide film with a thicknessof 6 μm and a Δn(a) of approximately 0.04 (a birefringent layer (a)),being laminated on the transparent film (b). This optical film includeda birefringent layer having an optical characteristic of nx>ny>nz.

EXAMPLE 5

75 weight parts of alternating copolymer (containing N-methylmaleimideof 50 mol %) synthesized from isobutene and N-methylmaleimide and 25weight parts of acrylonitrile-styrene copolymer containing 28 wt % ofacrylonitrile were dissolved in methylene chloride so as to prepare apolymer solution with the solid concentration of 15 wt %. This polymersolution was flow-expanded onto a polyethylene terephthalate (PET) filmarranged on a glass plate, and left for 60 minutes at room temperature.A polymer film formed on the PET film was peeled off and dried for 10minutes at 100° C., further 10 minutes at 140° C., and still further 30minutes at 160° C., so as to obtain a transparent film (b). The film hadan in-plane retardation value (Δnd=(nx−ny)×d) of 1 nm, and a retardationvalue (Rtn=(nx−nx)×d) of 4 nm in the thickness direction.

The thus obtained transparent film (b) was coated with the polyimidesolution as in Example 1, dried for 5 minutes at 100° C., and stretchedby 10% its original length by longitudinal uniaxial stretching at 130°C. so as to obtain an optical film. The optical film included acompletely transparent and flat mixed polymer film with a thickness of50 μm and a Δn(b) of approximately 0.001 (a transparent film (b)), and apolyimide film with a thickness of 6 μm and a Δn(a) of approximately0.035 (a birefringent layer (a)), being laminated on the transparentfilm (b). This optical film included a birefringent layer having anoptical characteristic of nx>ny>nz.

EXAMPLE 6

Polyimide as in Example 1 was dissolved in methyl isobutyl ketone so asto prepare a 25 wt % polyimide solution. This polyimide solution wascoated on a stretched TAC film as in Example 1, and dried for 5 minutesat 160° C. so as to obtain an optical film. The optical film included acompletely transparent and flat stretched TAC film with a thickness of75 μm and a Δn(b) of approximately 0.0006 (a transparent film (b)), anda polyimide film with a thickness of 6 μm a Δn(a) of approximately 0.04(a birefringent layer (a)), being laminated on the transparent film (b).This optical film included a birefringent layer having an opticalcharacteristic of nx>ny>nz.

EXAMPLE 7

A polyimide solution as in Example 1 was coated on an unstretched TACfilm with a thickness of 80 μm, and dried for 10 minutes at 100° C.,thereby obtaining an optical film. The optical film included acompletely transparent and flat TAC film with a thickness of 80 μm and aΔn(b) of approximately 0.0006 (a transparent film (b)), and a polyimidefilm with a thickness of 4 μm and a Δn(a) of approximately 0.025 (abirefringent layer (a)), being laminated on the transparent film (b).This optical film included a birefringent layer having an opticalcharacteristic of nx≈ny>nz.

COMPARATIVE EXAMPLE 1

A polynorbornene-based resin film having a An of approximately 0.002(trade name: ARTON film manufactured by JSR Corporation) stretched 1.3times its original length by fixed-end transverse stretching at 175° C.,thus obtained a film with a thickness of 80 μm. In an evaluation of thebirefringent index, this optical film had a birefringent characteristicof nx>ny>nz.

COMPARATIVE EXAMPLE 2

A polyimide solution as in Example 1 was coated on a glass plate anddried for 10 minutes at 100° C. so as to prepare a polyimide film.Subsequently, the polyimide film was peeled off from the glass plate sothat a completely transparent and flat film with a thickness of 7 μm anda ≢n of approximately 0.04 was obtained. This optical film had abirefringent characteristic of nx≈ny>nz.

COMPARATIVE EXAMPLE 3

A polyethylene terephthalate (PET) film with a thickness of 75 μm wasstretched 1.3 times of its original length in the transverse directionby fixed-end transverse stretching at 175° C. so as to obtain astretched PET film with a thickness of 75 μm. Then the stretched PETfilm was coated with the polyimide solution as in Example 1, and driedfor 5 minutes at 150° C., thereby obtaining an optical film. The opticalfilm included a completely transparent and flat stretched PET film witha thickness of 75 μm and a Δn(b) of approximately 0.08 (a transparentfilm (b)), and a polyimide film with a thickness of 6 μm and a Δn(a) ofapproximately 0.04 (a birefringent layer (a)), being laminated on thetransparent film (b). This optical film included a birefringent layerhaving an optical characteristic of nx>ny>nz.

COMPARATIVE EXAMPLE 4

The solution as in Example 3 was coated onto a stretched PET film ofComparative example 3, thereafter dried for 5 minutes at 150° C. so asto obtain an optical film. The optical film included a completelytransparent and flat stretched PET film with a thickness of 75 μm and aΔn(b) of approximately 0.08 (a transparent film (b)), and a polyetherketone film with a thickness of 10 μm and a Δn(a) of approximately 0.035(a birefringent layer (a)), being laminated on the transparent film (b).This optical film included a birefringent layer having an opticalcharacteristic of nx>ny>nz.

With regard to each of the birefringent layers of the optical filmobtained in Examples and Comparative examples, Δnd (=(nx−ny)×d), Rtn(=(nx−nz)×d), Nz (=(nx−nz)/(nx−ny)), thickness, and a precision oforientation axis were measured respectively. Except the birefringentlayer of Example 5, each of the birefringent layers is peeled from theoptical film in order to measure the birefringent layer alone. For themeasurement of the birefringent layer of Example 5, an optical film wasmanufactured under a similar condition except that the transparent film(b) used in Example 5 was replaced by a TAC film from which thebirefringent layer was peeled off. The results are shown in Table 1.TABLE 1 Thickness Precision of Δn(b) Δn(a) Δnd (nm) Rth (nm) Nz (μm)orientation axis Example 1 0.0006 0.045 135 270 2.0 6 −0.5-+0.5 Example2 0.0006 0.020 10 200 20 10 −0.5-+0.5 Example 3 0.0006 0.025 50 125 2.55 −0.5-+0.5 Example 4 0.0006 0.039 100 235 2.4 6 −0.5-+0.5 Example 50.001 0.035 80 210 2.6 6 −0.5-+0.5 Example 6 0.0006 0.038 70 230 3.3 6−0.5-+0.5 Example 7 0.0006 0.025 0.9 100 111.1 4 — Comparative — 0.00291 182 2.0 80 −2.5-+2.5 example 1 Comparative — 0.043 0.3 298 993.3 7 —example 2 Comparative 0.08 0.042 50 250 5.0 6 −0.5-+0.5 example 3Comparative 0.08 0.035 44 370 8.0 10 −0.5-+0.5 example 4

As shown in Table 1, the optical film of each Example satisfied all theformulae (I), (II) and (III), whereas none of the optical films ofComparative examples 1 to 4 satisfied the formula (I).

(Evaluation of Display Properties)

Each of the optical films obtained in Examples 1 to 7 and Comparativeexamples 1 to 4 was laminated on a commercially available polarizingplate (trade name: HEG1425DU manufactured by Nitto Denko Corporation)via an acrylic sticking agent so as to manufacture a polarizing plateintegrally laminated with an optical compensating layer. Here, each ofthe polarizing plate was laminated on the optical film, so that thepolarizing plate will face the transparent film (b) of the optical film.Furthermore, the laminated polarizing plate was attached to thebacklight side of a liquid crystal cell, so that the polarizing platewill be arranged on outermost side, thus a liquid crystal display wasmanufactured.

Thereafter, display properties of each liquid crystal display wereevaluated. As a result of the evaluation, by using the optical films ofExample 1 to 7, an excellent contrast and display uniformity wereobserved in a wide viewing angle when viewed in the front and obliquedirections, a rainbow-colored irregularity was restrained. Particularly,the rainbow-colored irregularity was sufficiently restrained andexcellent display quality was exhibited by using any of the opticalfilms of Examples 1-6 in which the formula (II) was 100 or lower. On theother hand, when using the optical films of Comparative examples, arainbow-colored irregularity was occurred due to the depolarization, andthus the displays were not recognized clearly. The above-stated resultsshow that, in contrast to the optical films of Comparative examples, anoptical film of the present invention, which satisfies all the formulae(I), (II) and (III), can provide a liquid crystal display with excellentdisplay property, restraining occurrence of the rainbow-coloredirregularity.

INDUSTRIAL APPLICABILITY

As mentioned above, an optical film of the present invention satisfyingthe formulae (I), (II) and (III) is thin and transparent, and also ithas an optical characteristic of nx>ny>nz and excellent opticalproperties. Therefore, an optical film of the present invention canrealize a thin liquid crystal display and a thin self-light-emittingdisplay which provide not only an excellent contrast in a wide viewingangle when viewed in the front and oblique directions, but also anexcellent display quality while restraining occurrence of therainbow-colored irregularity.

1. An optical film comprising a birefringent layer (a) and a transparent film(b), wherein the birefringent layer is laminated on the transparent film, satisfying all the following formulae (I), (II) and (III): Δn(a)>Δn(b)×10  (I) 1<(nx−nz)/(nx−ny)  (II) 0.0005≦Δn(a)≦0.5  (III) Δn(a) is a birefringent index of the birefringent layer (a) and Δn(b) is a birefringent index of the transparent film (b), respectively represented by the following equations: Δn(a)=[(nx+ny)/2]−nz Δn(b)=[(nx′+ny′)/2]−nz′, in the above formulae (II) and the above-stated equations, nx, ny and nz indicate respectively refractive indexes in an X-axis direction, a Y-axis direction and a Z-axis direction in the birefringent layer (a); nx′, ny′ and nz′ indicate respectively refractive indexes in an X-axis direction, a Y-axis direction and a Z-axis direction in the transparent film (b); and the X-axis corresponds to an axial direction exhibiting a maximum refractive index within a plane of the birefringent layer (a) and the transparent film (b), the Y-axis corresponds to an axial direction perpendicular to the X-axis within the plane, and the Z-axis corresponds to a thickness direction perpendicular to the X-axis and the Y-axis.
 2. The optical film according to claim 1, wherein the birefringent layer (a) is laminated directly on the transparent film (b).
 3. The optical film according to claim 1, wherein the birefringent layer (a) comprises a non-liquid crystal material.
 4. The optical film according to claim 3, wherein the non-liquid crystal material is at least one polymer material selected from the group consisting of polyamide, polyimide, polyester, polyetherketone, polyamide imide, and polyester imide.
 5. The optical film according to claim 1, obtained by coating the material of the birefringent layer (a) directly on the transparent film (b) having a shrinking property so as to form a coating film, and shrinking the coating film in accordance with the shrinkage of the transparent film (b).
 6. The optical film according to claim 5, wherein the transparent film (b) is shrunk by heat.
 7. The optical film according to claim 1, obtained by coating the material of the birefringent layer (a) directly on the transparent film (b) so as to form a coating film, and stretching both the transparent film (b) and the coating film concurrently.
 8. The optical film according to claim 1, further comprising at least one of an adhesive layer and a pressure-sensitive adhesive layer.
 9. The optical film according to claim 8, wherein at least one of the adhesive layer and the pressure-sensitive adhesive layer is laminated on an outer layer.
 10. A laminated polarizing plate comprising an optical film and a polarizer, wherein the optical film is of claim
 1. 11. A liquid crystal panel comprising a liquid crystal cell and an optical member arranged on at least one surface of the liquid crystal cell, wherein the optical member is the optical film according to claim
 1. 12. A liquid crystal display comprising a liquid crystal panel, wherein the liquid crystal panel is of claim
 11. 13. A self-light-emitting display comprising the optical film according to claim
 1. 14. A liquid crystal panel comprising a liquid crystal cell and an optical member arranged on at least one surface of the liquid crystal cell, wherein the optical member is the laminated polarizing plate according to claim
 10. 15. A liquid crystal display comprising a liquid crystal panel, wherein the liquid crystal panel is of claim
 14. 16. A self-light-emitting display comprising the laminated polarizing plate according to claim
 10. 